1. Field of the Invention
The present invention relates to a video correction apparatus and method in which hue, chroma, and luminance of a video signal are corrected, a video correction program, and a recording medium on which the program is recorded.
2. Description of the Related Art
There are various types of display for displaying a video signal, and chromaticity points of three primary colors disperse for various display types. Further chromaticity points disperse for displays of the same type. Furthermore even in the video signal generated by an image pickup apparatus, deviations of tone (hue or chroma) and/or gradation (luminance) occur because of dispersion of three primary colors in an image pickup apparatus or difference in image pickup condition. Then, it is sometimes necessary to correct the hue, chroma, and luminance.
Meanwhile, as a base band video signal, either three primary colors signals of red (R), green (G), blue (B), or luminance signal (Y), and two color difference signals (R-Y, B-Y, or Pb, Pr) are used. The signals displayed in the display are three primary colors signals of R, G, B. However, when it is necessary to correct the hue or chroma, the color difference signals are processed more easily than the three primary colors signals, and therefore the color difference signals are generally used as the signals to be subjected to the correction processing of the hue or chroma. It is to be noted that the three primary colors signals, and luminance and color difference signals can easily be converted to each other by linear matrix computation.
Examples of a related-art correction processing of the hue and chroma include one example of a computation processing represented by the following equations (1), (2). In the equations (1), (2), R-Y, B-Y denote the color difference signals before the correction, r-y, b-y denote the color difference signals after the correction, and A1, A2 are coefficients. As well known, two color difference signals are represented by a plane (color difference plane) including two axes crossing at right angles to each other. T1, T2 in the equations (1), (2) denote correction angles on the color difference plane.(b-y)=A1×cos(T1)×(B-Y)+A1×sin(T2)×(R-Y)  (1)(r-y)=−A2×sin(T1)×(B-Y)+A2×cos(T2)×(R-Y)  (2)
When the coefficients A1, A2 are different in the equations (1), (2), amplitudes (chroma) of the color difference signals r-y, b-y can individually be set. When the angles T1, T2 are different, rotation angles of the color difference signals R-Y, B-Y are different, and therefore the hue can non-uniformly be corrected. When the coefficients A1, A2 and angles T1, T2 are the same, the chroma and hue can uniformly be corrected. In any case, all regions on the color difference plane whose axes are two color difference signals change in the correction processing by the equations (1), (2).
As other related-art examples, and color correction circuits for correcting the hue and chroma in a specific range, there are Japanese Patent Application Laid-Open Nos. 10(1998)-145805 and 2001-128189.
Since the whole hue is corrected in the related-art correction processing by the equations (1), (2), there is a serious disadvantage that the hue or chroma cannot be corrected only in a specific angle region on the color difference plane as a specific hue region. The color correction circuit described in the Japanese Patent Application Laid-Open No. 2001-128189 is an example of the correction processing in which this disadvantage is avoided. According to this color correction circuit, only the specific angle region is set as the correction region, and the hue or chroma of pixels in the correction region can be corrected.
However, the color correction circuit of the above-described publication has a problem that the hue of all the pixels in an angle region surrounded with two isochromatic lines is corrected in a direction crossing at right angles to an isochromatic line which is a center line of the two isochromatic lines, and the chroma of all the pixels is corrected in a direction parallel to the center isochromatic line. When the angle region as the correction region is enlarged, the hue or chroma is exactly corrected in the vicinity of the center isochromatic line, but the hue or chroma cannot exactly be corrected in a region distance from the center isochromatic line. Therefore, there is a problem that a broad angle region cannot be the correction region.
Moreover, there is a problem that the hue or chroma can be corrected, but the luminance signal (gradation) cannot be corrected in accordance with the correction of the hue or chroma. Furthermore, when the luminance signal is corrected, the chroma apparently changes. Therefore, the chroma has to be also corrected in accordance with the correction of the luminance signal, but there is a problem that the chroma changing with the correction of the luminance signal cannot be corrected.
In the related art, a practical video correction apparatus and method or a video correction program has not heretofore been found in which the hue, chroma, and luminance can be corrected to be optimum in consideration of balance of video and/or each element of the hue, chroma, and luminance can freely be corrected. There has increasingly been a demand for a higher image quality with respect to an image to be displayed in the display, and there has been a sincere demand for a video correction apparatus and method or video correction program in which the video can arbitrarily be corrected to be optimum. At this time, the video correction apparatus and method or video correction program can preferably be realized easily and inexpensively without complicating a constitution or step.